Small vibration motor and method of manufacturing the same

ABSTRACT

A driver IC and passive parts, which convert a direct current voltage into a three-phase voltage, and an FP coil for cyclically generating a magnetic field through the driver IC are mounted on a flexible substrate, which constitutes a small vibration motor. The driver IC is a so-called bare chip in which a circuit section is exposed and is not molded with resin and the like. Magnets and an unbalance weight are installed on a yoke having a shaft. The FP coil and the magnet are placed so as to face each other. A cover is caulked to fixed to a bottom plate. Thus, the vibration motor can be miniaturized and thinned. Moreover, the vibration motor can be automatically manufactured, and installing them to an electronic apparatus can be automatically performed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present document is based on Japanese Priority DocumentJP2002-220889, filed in the Japanese Patent Office on Jul. 30, 2002, theentire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small vibration motor, which is builtin an electronic apparatus such as a mobile telephone, a PDA and thelike, for generating vibrations, and to a method of manufacturing thesame.

2. Description of Related Art

Conventionally, the electronic apparatus such as the mobile telephone,the PDA and the like includes the mechanism of a so-called silent modeto notify an incoming call through vibrations, and an alarm to notify apredetermined time through vibrations, and the like. As a mechanism forgenerating a vibration, a vibration actuator is built in such anelectronic apparatus.

FIG. 14A is a schematic view showing the inner structure of a mobiletelephone in which a vibration motor serving as a conventional vibrationactuator is built in. FIG. 14B is a schematic view showing theappearance of the vibration motor. As shown in FIG. 14A, printed circuitboards (motherboards) 101, 102 are mounted within the mobile telephone100. A speaker 103 and a vibration motor 104 are connected to the sideof the printed circuit board 101. The vibration motor 104 is driven by adriver IC 105 mounted on the printed circuit board 101. On the otherhand, a power supply IC 110, a converter IC 111, an MPU 112, a memory IC113 and the like are mounted on the side of the printed circuit board102.

The illustrated vibration motor 104 is the motor with a brush. As shownin FIG. 14B, a weight 125 is fixed around an output shaft 120. When thevibration motor 104 is driven, the output shaft 120 is rotated, and theweight 125 is eccentrically rotated. The eccentric rotation of theweight 125 causes a rotational unbalanced energy to be generated as avibration component.

SUMMARY OF THE INVENTION

Conventionally, when the motor with a brush is used as the vibrationmotor, the rotational defect caused by so-called slit-short can not bemade zero. Thus, this has a problem in a reliability of a vibrationgeneration operation.

Also, in view of the internal volume of a portable apparatus and thelike, it is naturally desired to have a smaller vibration motor. A motorbody can be reduced to, for example, a diameter of about 3.5 mm.However, a problem may occur if the diameter of the motor body is madesmaller. That is, the diameter of the weight for generating therotational unbalanced energy becomes too small to generate enoughvibrations, thus the vibration component decreases. In particular,recently, the portable apparatus such as the mobile telephone, the PDAand the like tends to be thinned. Accordingly, this causes a problemthat fitting a cylindrical vibration motor to such thinned portableapparatus is difficult.

Further, from the viewpoint of the battery life of the portableapparatus such as the mobile telephone and the like, the electric powerconsumption is obviously desired to be lower. However, this has aproblem that the miniaturization of the motor body brings about theincreases in the rotational number and the electric power consumption.

Moreover, the assembly of the conventional vibration motor into theelectronic apparatus must rely on a man power. Thus, the automationthereof is difficult.

Accordingly, there has been a need to provide a smaller vibration motorthat may be miniaturized and thinned and automatically assembled into anelectronic apparatus, and a method of manufacturing the same.

In order to attain the above-mentioned subjects, a small vibration motoraccording to the present invention is characterized by including: arotor yoke in which an unbalance weight and a magnet are placed and isfixed to a shaft; a driving torque generating coil that is placed on asubstrate so as to face the magnet; driving electronic parts placed onthe substrate, which includes an integrated circuit composed ofnon-molded bare chips, supplies an alternating current to the drivingtorque generating coil to rotate the rotor yoke around the shaft; abottom plate which supports the substrate and to which a radial bearingthat the shaft is engaged with is fixed; and a cover for covering therotor yoke, the driving torque generating coil and the drivingelectronic parts, which is adhered to the bottom plate.

Also, as the preferable embodiment, in the small vibration motor, thesubstrate may be constituted by a flexible substrate, and the drivingtorque generating coil may be electrically connected to the flexiblesubstrate through three terminals.

Also, as the preferable embodiment, the small vibration motor mayinclude a terminal that is formed on a substrate protruded from thepackage, and engaged with a connector mounted on a motherboard, andthereby electrically connected.

Also, as the preferable embodiment, the small vibration motor mayinclude a terminal that is placed in the cover or the bottom and engagedwith a socket mounted on a motherboard and thereby electricallyconnected.

Also, as the preferable embodiment, the small vibration motor mayinclude a land which is formed on a surface of the cover or the bottomin contact with a motherboard, and electrically connected to anotherland formed on the motherboard.

In order to attain the above-mentioned subjects, a method ofmanufacturing a small vibration motor according to the present inventionis characterized by including the steps of: mounting driving electronicparts and a driving torque generating coil on a board; placing a magneton a rotor yoke so as to face the driving torque generating coil, in arotor composed of the rotor yoke and a shaft; placing an unbalanceweight at a part of the rotor yoke; fixing a radial bearing to a bottomplate; installing a bottom plate, on which the radial bearing is placed,to the substrate; installing the rotor to the radial bearing which isengaged with the shaft; and packaging by covering the substrate, thedriving electronic parts and the rotor with a cover, and adhering thecover to the bottom plate.

Also, as the preferable embodiment, the method of manufacturing thesmall vibration motor may be characterized in that as the drivingelectronic parts, at least an integrated circuit composed of non-moldedbare chips is mounted on the substrate.

Also, as the preferable embodiment, the method of manufacturing thesmall vibration motor may be designed such that the board is constitutedby a flexible substrate, and the driving torque generating coil iselectrically connected to the flexible substrate through threeterminals.

Also, as the preferable embodiment, the method of manufacturing thesmall vibration motor may include a step of forming a terminal on asubstrate protruded from the package, which is engaged with a connectormounted on a motherboard and thereby electrically connected,.

Also, as the preferable embodiment, the method of manufacturing thesmall vibration motor may include a step of placing a terminal, which isengaged with a socket mounted on a motherboard and thereby electricallyconnected, on the package.

Also, as the preferable embodiment, the method of manufacturing thesmall vibration motor may include a step of forming a land on a surfacein contact with the motherboard of the package, which is electricallyconnected to another land formed on a motherboard.

In the present invention, the driving electronic parts and the drivingtorque generating coil are mounted on the board. In the rotor composedof the rotor yoke and the shaft, the magnets are placed so as to facethe driving torque generating coil in the rotor yoke. The unbalanceweight is placed at a part of the rotor yoke. The radial bearing isfixed to the bottom plate. The bottom plate on which the radial bearingis placed is installed to the board. The shaft is engaged with theradial bearing, and the rotor is also installed on the radial bearing.Moreover, the board, the driving electronic parts and the rotor arecovered with the cover. Then, the cover is adhered to the bottom plateto be packaged. Thus, the vibration motor can be miniaturized andthinned. Moreover, the manufacturing process of the vibration motor andmounting the motor to an electronic apparatus are possible to be carriedout automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe presently preferred exemplary embodiments of the present inventiontaken in conjunction with the accompanying drawings, in which:

FIGS. 1A, 1B are schematic views showing a structure of a smallvibration motor according to an embodiment of the present invention;

FIGS. 2A to 2D are conceptual views showing a process for manufacturinga driver IC 4.

FIG. 3 is a flowchart showing a process for manufacturing a smallvibration motor;

FIG. 4 is a flowchart showing a process for manufacturing a smallvibration motor;

FIG. 5 is a flowchart showing a process for manufacturing a smallvibration motor;

FIG. 6 is a flowchart showing a process for manufacturing a smallvibration motor;

FIGS. 7A, 7B are schematic views explaining a process for manufacturinga small vibration motor;

FIGS. 8A to 8C are schematic views explaining a process formanufacturing a small vibration motor;

FIGS. 9A to 9C are schematic views explaining a process formanufacturing a small vibration motor;

FIGS. 10A to 10C are schematic views explaining a process formanufacturing a small vibration motor;

FIGS. 11A to 11C are schematic views explaining a process formanufacturing a small vibration motor;

FIGS. 12A to 12C are schematic views showing an example of a method ofmounting a small vibration motor 30 onto a motherboard;

FIG. 13 is a schematic view showing an example of shipping/deliveringmanner of the small vibration motor 30; and

FIGS. 14A, 14B are schematic views showing the inner structure of amobile telephone in which a vibration motor serving as a conventionalvibration actuator is built.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below withreference to the attached drawings.

A. Structure of Small Vibration Motor

FIGS. 1A, 1B are schematic views showing the structure of a smallvibration motor according to the embodiment of the present invention. AnFP (Flexible Printed) coil 1 and a magnet 2 are placed facing eachother. The FP coil 1 is constituted by a wiring layer composed of aplurality of layers. A signal inputted through a flexible substrate 3 isconverted into a three-phase voltage by a driver IC 4 so that a magneticfield is cyclically generated. The magnet 2 is linked to a yoke 6 havinga shaft 5. The rotational magnetic field of the FP coil 1 rotates themagnet 2 and the yoke 6. An unbalance weight 7 is eccentricallyinstalled to the yoke 6. The rotation of the unbalance weight 7generates an unbalanced component to thereby generate a vibration.

Notches 10 are formed at the four corners of the FP coil 1, and theflexible substrate 3 is exposed there. The driver IC 4, passive parts(C, R) 11 and the like are mounted on the notches 10. The flexiblesubstrate 3 is made of polyimide as the base material, and that wiringsurface is treated with Cu+Ni+Au.

The shaft 5 is supported by a radial bearing 13 installed to a bottomplate 12, a thrust bearing 14 and a thrust bearing holder 15. The radialbearing 13 is made of sintered metal in which, for example,copper-based, iron-steel-based or iron-based oil is impregnated, and itis the cylindrical shaped member. Incidentally, the radial bearing 13may be made of resin.

Also, a cover 16 is caulked and soldered and thereby fixed to the bottomplate 12. The top surface of the cover 16 is flat such that the smallvibration motor can be assembled (absorbed) by a robot arm and the likewhen it is mounted onto the motherboard. Also, a part of the flexiblesubstrate 3 is protruded so as to be wired to the motherboard. However,having this protrusion is not the essential condition.

The small vibration motor according to this embodiment as mentionedabove has the approximate dimension of 8.6×8.6 mm, the thickness of 1.9mm, and the volume is about 140 mm³. The conventional motor with thebrush has the dimension of about 300 to 500 mm³. Thus, as compared withthe conventional motor, the small vibration motor according to thisembodiment can be reduced its volume substantially equal to ½ to ⅓.

B. Process for Manufacturing Small Vibration Motor

The process for manufacturing the above-mentioned small vibration motorwill be described below. Here, FIGS. 2A to 2D are the conceptual viewsshowing the process for manufacturing the driver IC 4. Also, FIGS. 3 to6 are the flowcharts showing the entire process for manufacturing thesmall vibration motor. Moreover, FIGS. 7A to 11C are the schematic viewsexplaining the process for manufacturing the small vibration motor.

B-1. Process for Manufacturing Driver IC

At first, as shown in FIG. 2A, the necessary circuit is formed on a Siwafer 20 by a typical process such as a photo processing and the like.After that, as, shown in FIG. 2B, protrusion electrodes 21 are formedthereon. Next, as shown in FIG. 2C, chips are diced one by one, and madeinto pieces by an extension ring 22, as shown in FIG. 2D. The driver ICis not a typical package IC (an IC molded with resin and the like), butit is a so-called bare chip in which a circuit section is exposed. Also,the protrusion electrode 21 can be formed by an Au plating, a Niplating, an Au stud bumping method, or a solder bumping method or thelike. Such a protrusion electrode can be flexible about the supplyingcondition and the inspecting method of the wafer.

B-2. Flexible Substrate Process

On the other hand, a flexible substrate manufactured in a different step(not shown) is prepared (Step S10 in FIG. 3). At first, as shown in FIG.7A, the driver IC (bare chip) 4 and the passive elements (C, R) 11 areplaced at predetermined positions on the flexible substrate 3. Soldering(reflow) is performed thereon, and flux components contained in pasteare washed. Then, underfill resin is coated to mechanically reinforcethe driver IC 4. Again, the resin is cured at a thermally curing process(Step S12). Next, as shown in FIG. 7B, the FP coil 1 manufactured in adifferent process is placed at a predetermined position, and soldering(reflow) is performed thereon (Step S14).

There are three connection portions between the FP coil 1 and theflexible substrate 3, and there are also only three connection terminalsto the motherboard (not shown) through the flexible substrate 3. Thus,although the vibrating section and the driver IC 4 are electricallyconnected, this is not a strong vibrator, and this has the action ofattenuating the vibration generated by the flexible substrate 3 itself.Hence, it is possible to suppress the mechanical stress on the mountedportion. Then, the circuit is inspected (Step S16). If the circuitcontains any repairable defect, it is returned to the step S12 in orderto repair it by carrying out the soldering once again and the like, andthen is re-inspected. On the other hand, if it contains any defect thatcan not be repaired, it-is discarded (Step S18). Also, if the inspectedresult is satisfactory, the operational flow proceeds to a next process,which will be described-later.

B-3. Process for Installing Radial Bearing

A bottom plate is prepared in order to package the small vibration motor(Step S20 in FIG. 4). The bottom plate 12 is manufactured by performinga rolling process on an aluminum plate and the like. At first, as shownin FIG. 8A, the radial bearing 13 is installed onto the bottom plate 12(Step S22). Then, as shown in FIGS. 8B to 8C, the thrust bearing 14 andthe thrust bearing holder 15 are installed (Step S24) and caulked andthereby fixed (Step S26). Next, whether or not the radial bearing 13,the thrust bearing 14 and the thrust bearing holder 15 are rightlyinstalled is inspected (Step S28). Here, if any of them has a defect, itis discarded (Step S30). On the other hand, if they have no defect, theoperational flow proceeds to a next process which will be describedlater.

B-4. Rotor Yoke Process

The rotor yoke 6 is prepared (Step S40 in FIG. 5). As shown in FIG. 9A,the magnets 2 are adhered (Step S42). Then, the magnets 2 are magnetized(Step S44). As shown in FIG. 9B, the shaft 5 is pressed into the rotoryoke 6 (Step S46). Then, as shown in FIG. 9C, the unbalance weight 7 isadhered and caulked and thereby fixed to the rotor yoke 6 (Step S48).

B-5. Assembling Process

Next, as shown in FIGS. 10A and 10B, the flexible substrate 3 formed bythe above-mentioned flexible substrate process, on which the parts aremounted, is adhered on the bottom plate 12 manufactured by the processfor installing the radial bearing as mentioned above. (Step S50 in FIG.6). Next, as shown FIG. 10B, the shaft 5 and the rotor yoke 6manufactured by the above-mentioned rotor yoke process are installed tothe radial bearing 13 (Step S52). Next, as shown in FIG. 10C, thedifferently manufactured cover 16 is caulked and thereby fixed to thebottom 12 (Step S54), and a terminal to be electrically connected to themotherboard is soldered to the protrusion portion of the flexiblesubstrate 3 (Step S56). Then, the appearance check and the electricalinspection are carried out (Step S58). If there is any defect, thevibration motor is discarded (Step S60). On the other hand, there is nodefect, the vibration motor is shipped (Step S62). The manufacturing thesmall vibration motor 30 is completed as described above.

The small vibration motor 30 according to the above-described embodimentcan be miniaturized and thinned. As compared with a conventional motorwith the brush, the longitudinal and lateral dimension of the smallvibration motor 30 is about 8.6×8.6 mm, and its thickness is about 1.9mm, and its volume is about 140 mm³. Thus, this has the volumesubstantially equal to ½ to ⅓ of the conventional motor. In addition,the driver IC can be mounted as the bare chip, it is advantageous thatthe chip manufacturing processes may be reduced. Further, the rotationof the rotor yoke 6 inside helps to increase the cooling efficiency.

Also, since the vibration motor 30 has the driver IC 4 therein, mountingon the motherboard (not shown) can be treated as similarly to mountingthe surface mount parts. At this time, the mounted direction of thesmall vibration motor 30 needs to be recognized. In order to indicatethe mounting direction, a simple mark 31 may be printed as shown inFIGS. 11A and 11B, or a part of the outer surface may be cut away as anotch 32, as shown in FIG. 11C.

In addition, as the method of mounting the small vibration motor 30 onthe motherboard, there are: a manner of using an FPC (Flexible PrintedCircuit Board) connector 40 electrically connected to the terminalformed on the protrusion section of the flexible substrate 3, as shownin FIG. 12A; a manner of using sockets 41 that is engaged with aterminal placed in a package to be electrically connected, as shown inFIG. 12B; and a manner of forming lands 42 on the rear surface of thesmall vibration motor 30 to mount on the motherboard like the surfacemount part. In these ways, it is possible to flexibly address a requestfrom a client.

Also, as parts shipment/delivery manner of the vibration motor 30, it ispossible to pack them as a reel-shaped tape 50 as shown in FIG. 13, itenables to manage the parts easier. The small vibration motor 30 isstored in a small vibration motor storing portion 51 of the reel-shapedtape 50 which has reel wheel holes 52.

Finally, the embodiments and examples described above are only examplesof the present invention. It should be noted that the present inventionis not restricted only to such embodiments and examples, and variousmodifications, combinations and sub-combinations in accordance with itsdesign or the like may be made without departing from the scope of thepresent invention.

1-5. (canceled)
 6. A method of manufacturing a small vibration motor,comprising the steps of: mounting driving electronic parts and a drivingtorque generating coil on a substrate; placing a magnet on a rotor yokein a rotor comprising said rotor yoke and a shaft so as to face saiddriving torque generating coil; placing an unbalance weight at a part ofsaid rotor yoke; fixing a radial bearing to a bottom plate; installing abottom plate, on which said radial bearing is placed, to said substrate;installing said rotor to said radial bearing which is engaged with saidshaft; and packaging by covering said substrate, said driving electronicparts and said rotor with a cover, and adhering said cover to saidbottom plate.
 7. The method of manufacturing the small vibration motor,according to claim 6, wherein as said driving electronic parts, at leastan integrated circuit comprising non-molded bare chips is mounted onsaid substrate.
 8. The method of manufacturing the small vibrationmotor, according to claim 6, wherein said substrate comprises a flexiblesubstrate, and said driving torque generating coil is electricallyconnected to said flexible substrate through three terminals.
 9. Themethod of manufacturing the small vibration motor, according to claim 6,further comprising a step of forming a terminal on a substrate protrudedfrom said package, which is engaged with a connector mounted on amotherboard, and thereby electrically connected.
 10. The method ofmanufacturing the small vibration motor, according to claim 6, furthercomprising a step of placing a terminal on said package, which isengaged with a socket mounted on a motherboard, and thereby electricallyconnected.
 11. The method of manufacturing the small vibration motor,according to claim 6, further comprising a step of forming a land on asurface in contact with said motherboard of said package, which iselectrically connected to another land formed on a motherboard.